Here is the idea: who needs MDI, ever? Why torturing yourself and scaring off your users?
Do yourself a great favor: do not use MDI at all. You can do much easier to implement design without it, with much better quality. MDI is highly discouraged even by Microsoft, in fact, Microsoft dropped it out of WPF and will hardly support it. More importantly, you will scare off all your users if you use MDI. Just don't. Please see:http://en.wikipedia.org/wiki/Multiple_document_interface#Disadvantages
],How to Create MDI Parent Window in WPF?
I can explain what to do instead. Please see my past answers:How to Create MDI Parent Window in WPF?
],Question on using MDI windows in WPF
],MDIContainer giving error
],How to set child forms maximized, last childform minimized